In the manufacture both of vehicles and exterior mounted components or else machinery and equipment, instead of or in combination with conventional joining techniques such as screwing, riveting, punching or welding, the use of high-grade adhesives is becoming ever more frequent. When structural parts are adhesively bonded, high strength and impact resistance on the part of the adhesive are of the utmost importance.
Conventional epoxy adhesives are indeed distinguished by a high mechanical strength, more particularly a high tensile strength. When the adhesive bond is subject to shock-like stress, however, typical epoxy adhesives are usually too brittle and under crash conditions, where there are great tensile stresses and also great peel stresses, they may fall well below the requirements, more particularly those of the automobile industry. Often unsatisfactory in this respect, in particular, are the strengths at high temperatures but more particularly those at low temperatures as well, below −10° C.
Consequently, a variety of methods has been employed with the aim of improving the impact resistance of thermosetting epoxy adhesives.
EP-A-1 359 202 describes an improvement to impact resistance through the use of a urea derivative in a nondiffusing carrier material, and also impact-resistant compositions which comprise said urea derivative and also epoxide adducts. EP-A-1 431 325 describes the use of an epoxide-group-terminated impact-modified polymer and also impact-resistant compositions which comprise said impact-modified polymer and also epoxide adducts. EP-A-1 498 441 likewise describes a further epoxide-group-terminated impact-modified polymer and also impact-resistant compositions which comprise said impact-modified polymer and also epoxide adducts. Through the use of the epoxide-group-terminated impact-modifier polymers it has indeed been possible to achieve a marked increase in the impact resistance at low temperatures; however, all of the impact-resistant compositions disclosed in these documents contained an epoxide adduct. Such epoxide adducts require separate preparation and tend to have a relatively high viscosity.